1. Field of the Invention
The present invention relates to a base station apparatus in a 1×EV-DO system and a method thereof that determine different reverse rates for different data transmission situations of each mobile station.
2. Background of the Related Art
In general, an IS-95 based mobile communication system provides voice-centered services. Recently, however, thanks to the development of 1×EV-DO wireless protocol, which is a forward link providing the maximum 2.4576 Mbps high speed packet data service, the mobile communication system is now able to provide multimedia services, such as IMT-2000 service as well as high speed packet data service, moving image service, and further packetized voice service.
The 1×EV-DO system is not focused on providing voice-centered services like IS-95. Rather, it is aiming to provide high speed packet data services only. Specifically, the data source of each mobile station varies depending on the wireless environment. The high speed data in a forward link is first loaded into a time slot that is segmented into 1.67 ms units and is transmitted through time division communication.
The reverse rates in the 1×EV-DO system are 9.6 Kbps, 19.2 Kbps, 38.4 Kbps, 76.8 Kbps, and 153.6 Kbps. The mobile station often changes the reverse rate to determine an appropriate rate in accordance with a reverse activity bit and a random number. The random number is based on a reverse rate limit that is included in a broadcast reverse rate limit message and transmitted from the base station. The reverse rate limit is pre-defined in a manner that it is designated according to an active call.
Related art reverse rate limits of the mobile stations are designated according to the number of mobile stations supporting active calls, in a sector where the reverse rate limit message is broadcasted. In other words, if the number of active calls in a sector is low, the base station employing a related art 1×EV-DO system, to maximize reverse link throughput, selects a high reverse rate limit. On the other hand, if the number of active calls in a sector is high, the reverse rate limit is set low to reduce the reverse link loading.
FIG. 1 is a block diagram illustrating an apparatus for determining the reverse rate in a related art mobile communication. The device includes a plurality of mobile stations 11 and a base station 12 that generates and transmits a broadcast reverse rate limit message. Base station 12 has a reverse rate generation module 12a that generates a broadcast reverse rate limit message by selecting a reverse rate limit per active mobile station using a mapping table (refer to FIG. 2). The mapping table associates reverse rate limits with the numbers of active calls. After a reverse rate limit is selected, reverse rate generation module transmits the broadcast reverse rate limit message to every active mobile station. All mobile stations in the active state receive the same reverse rate limit. Reverse rate generation module 12a calculates the number of active calls for each mobile station that transmits reverse data. Then, using the mapping table, reverse rate generation module 12a sets the reverse rate limit, corresponding to the calculated number of active calls, and assigns this limit to each mobile station. For instance, suppose the present number of active calls in the sector is 5. Then, based on the associated limit in the mapping table, reverse rate generation module 12a designates 38.4 Kbps as the reverse rate limit for each of the five mobile stations. Therefore, the broadcast reverse rate limit message including the reverse rate limit, 38.4 Kbps, is transmitted to the five active mobile stations.
FIG. 2 illustrates a mapping table associating the reverse rates with the number of the active calls in the related art mobile communication system. The number of active calls in the mapping table ranges from 1 to 8, and a reverse transmit limit is associated with each number of active calls. For example, if the number of active calls is 1, the reverse rate limit is 153.6 Kbps, which is the maximum value applicable to the 1×EV-DO system. As the number of active calls increases, the reverse rate limit decreases. In this manner, the minimum reverse rate, 9.6 Kbps, is associated with 8 active calls. FIG. 2 is just one example of the mapping table. Thus, even when the number of active calls exceeds 5, it is possible to make a different mapping between the number of active calls and the reverse rate limit.
FIG. 3 is a flow chart showing a method for generating a broadcast reverse rate limit message in the related art. Base station 12 calculates the number of active calls based on the active calls requested from each mobile station 11. Then, base station 12 determines the reverse rate limit corresponding to the calculated number of active calls, using the mapping table (S31).
Afterwards, base station 12 determines whether an index, having values that identify each mobile station 11 uniquely and that have been assigned to each active state mobile station, is set to identify the maximum reverse power control (RPC) value (S33). Base station 12 repeatedly generates a reverse rate limit message for every index value, using the reverse rate limit determined in the step 31, until the index reaches the maximum RPC value (S35). Each index value is pre-assigned to a mobile station. Also, the maximum RPC can be designated as 32. Thus, it is possible to identify each mobile station based on the index value, and when the reverse rate limit message generated is transmitted to every mobile station later, the index can be used for transmitting the reverse rate limit message to each mobile station.
When the index value exceeds the maximum RPC, base station 12 transmits the reverse rate limit message generated for index values 0 through 31 to each mobile station (S37). The reverse rate limits included in the reverse rate limit messages, transmitted to all mobile stations, hold an equivalent value. Steps 31 through 37 can be repeated for every transmission cycle of the reverse rate limit.
The above-described method of applying the reverse rate limit, determined according to the number of active calls to all active state mobile stations, does not consider the transmission state of each mobile station. That is to say, although there may be a great number of active calls and some mobile stations may have large volumes of data to transmit, if a low reverse rate limit is applied to every mobile station equally, the mobile stations with large volumes of data to transmit will not be able to secure a transmission rate high enough to transmit all the data. This consequently lowers the usage efficiency of the reverse link greatly.
The above references are incorporated by reference herein where appropriate for appropriate teachings of additional or alternative details, features and/or technical background.